The (NN-dialkyldithiocarbamato)nitrosyl-compounds, M(NO)2(S2CNR2)2, (M = Mo, R = Me or Et; M = W, R = Me) and Mo(NO)(S2CNR2)3(R = Me, Et, Prn, or Bun) have been prepared from the reaction of [M(NO)2Br2]n and [Mo(NO)Cl3]n with the appropriate sodium dialkyldithiocarbamate. From i.r. and mass spectral data it is shown that the dinitrosyl compounds are monomeric and have cis- octahedral structures (symmetry C2). The mononitrosyl molybdenum compounds, Mo(NO)(S2CNR3)3, differ from the formally analogous ruthenium compounds, Ru(NO)(S2CNR2)3, in that the former contains three bidentate sulphur ligands whereas the latter contains two bidentate and one monodentate sulphur ligand. N.m.r. data obtained from the complexes are discussed in terms of hindered rotation about the S2C–NR2 bond and may be used as an indication of C–N partial double-bond character.